For those who are new to the hobby, do take a look at the link below to understand more about beetles!

Substrate for larvae

The following section regarding substrate for larvae can be slightly technical and dry but is crucial to raising beetles well. Quoting from Taiwanese breeder, "Teacakes":

"Stag beetles in general require a substrate that is of a lower degradation. While rhinos require substrate of a higher degradation.  Flower beetles in general will survive in almost all substrate. 

In Taiwan, lower degradation substrate are made from fermenting sawdust. We normally will label such products as 木屑. Higher degradation substrate here are mostly made of waste kinshi from mushroom farms. We normally label them as 土.

When raising larvae, try to understand the favoured degradation range of the species you are raising. Use substrate that is closer to the lowest acceptable degradation to fill containers. This increases the amount of time the substrate in each container will stay in the acceptable range. This in turn reduces the frequency of substrate change, thus reducing disturbance of larvae. Something to note, substrate degrades slower in a cooler environment, so providing a climate controlled environment not only makes the larvae feel less stress, it also prolongs the usefulness of the substrate. 

Something else I feel I should mention is that, if you are using kinshi to raise stag beetles, climate control is very important. As kinshi is alive, it will produce heat. On hot days if left at room temperatures in Singapore, it can reach temperatures of 35 to 37 degree Celsius. This will be fatal to most if not all larvae."

To further elaborate, kinshi refers to sawdust that has been colonized by mushroom mycelium. Stag beetles cannot digest raw sawdust because of a component in the wood called lignin. The mushroom mycelium decomposes lignin in the wood, which allows stag beetle larvae to easily digest the wood. Do note that not all species of larvae are suitable to be fed kinshi.